Experiments are proposed to examine several aspects of the immunobiology of the host-parasite relationship in experimental Chagas' disease (American trypanosomiasis). In a continuation of previous studies, the cellular basis of immunosuppression in mammals infected with Trypanosoma cruzi will be examined with special emphasis on T helper cells and their effector functions as related to their production and sensitivity to interleukin 2. The role of T cells with phenotypes indicative of suppressor and cytotoxic T cells will be examined in an attempt to determine the role of these sub-populations of lymphocytes. Studies with T helper cells (L3T4) and Lyt 2,3+ T cells and be performed using long-term T cell lines and/or clones in vitro and in vivo. There effects will be assessed by their ability to affect longevity and parasitemia in highly susceptible and resistant strains of mice. Experiments and also planned to re-examine the role and significance of antibody-dependent, complement-mediated effector functions in lysis of trypomastigotes of T. cruzi as recent results suggest that the significance of antibody in immunity to T. cruzi is highly dependent on the strain of parasite used in such studies.